An anthropic understanding of the cosmological constant requires that the vacuum energy at late time scans from one patch of the universe to another. If the vacuum energy during inflation also scans, the various patches of the universe acquire exponentially differing volumes. In a generic landscape with slow-roll inflation, we find that this gives a steeply varying probability distribution for ...

We explore the qualitative changes that would occur if the amplitude Q ∼ 10 of cosmological density fluctuations were different. If Q ∼< 10 , the cosmological objects that form would have so low virial temperatures that they may be unable to cool and form stars, and would be so loosely bound that even if they could produce a supernova explosion, they might be unable to retain the heavy elements...

The standard model of particle physics contains Ngen = 3 generations of quarks and leptons, i.e., two sets of three particles in each sector, with the two sets differing by 1 unit of charge in each. All 12 “predicted” particles are now experimentally accounted for, and there are strong (though not air-tight) arguments that there are no more than three generations. The question is: why exactly N...

It is conceivable that some of the properties of the physical world might not be uniquely determined by an underlying dynamical principle, but might instead reflect the requirement that those properties be compatible with the existence of intelligent observers like us, capable of studying them. In modern theoretical physics, this controversial idea is called the “anthropic principle” [1]. Broad...

When reasoning about self-locating belief, one should reason as if one were a randomly selected bit of information. This principle can be considered to be an application of Bostrom’s Strong Self-Sampling Assumption(SSSA)[2] according to which one should reason as if one were a randomly selected element of some suitable reference class of observer-moments. The reference class is the class of all...

The Epistemic Objection says that certain theories of time (like the “growing block” and “moving spotlight”) imply that it is impossible to know which time is absolutely present. Standard presentations of the Epistemic Objection are elliptical—and some of the most natural premises one might fill in to complete the argument end up leading to radical skepticism. But there is a way of filling in t...

We discuss the anthropic principle when applied to the holographic dark energy. We find that if the amplitude of the density fluctution is variable, the holographic dark energy fares better than the cosmological constant.

Even when completely and consistently formulated, a fundamental theory of physics and cosmological boundary conditions may not give unambiguous and unique predictions for the universe we observe; indeed inflation, string/M theory, and quantum cosmology all arguably suggest that we can observe only one member of an ensemble with diverse properties. How, then, can such theories be tested? It has ...